Sometimes a player will have multiple voluntary effects (such as Tactics Cards and/or Order Abilities) with the same triggering event (such as “When a friendly unit attacks” or “Start of the round”). In these situations, that player may only ever use 1 voluntary effect in response to that trigger.
Player A has a Tactics card that triggers When a friendly unit attacks. One of their Attachments also has an Order Ability that triggers When a friendly unit attacks. When their unit attacks, they may only select 1 of these effects to activate.